Classically there are considered to be three components of effective pitching (a) the speed of the ball, (b) the location of the pitch as it travels over the plate and (c) movement of the ball from it's natural path of travel. The radar gun attempts to provide only one of these, (a) above, and is not considered extremely accurate. Several approaches have been tried using a matrix and/or planes of light beams to measure both speed, (a) above, and position, (b) above, but each has limitations, solved by the approach described here.
U.S. Pat. No. 3,229,975, issued January 1966, used a matrix of horizonal and vertical light beams in an attempt to measure the position and speed of a ball and display same. No attempt was made to shield ambient light interference and isolation between the beams were not indicated.
U.S. Pat. No. 4,563,005, issued January 1986, describes a method of scanning an array of emitters and coordinating the timing with signals received by four high frequency receivers, spaced at the corners, to form a plane. Two of these planes are described as separated in an attempt to measure speed between planes. No claim was made to avoid external interference from ambient sources.
U.S. Pat. No. 5,230,505, issued July 1993, describes using two planes of sensors which are sourced by continuously radiating infrared emitters and provides a formula of measured times to calculate speed. The claims state the inter-sensor spacing as approximately 2 inches which allows for a position tolerance in excess of 1 inch. This variation in position will also induce an error into the speed calculation. Further, the method of reducing ambient light is to enclose the complete apparatus, greatly reducing its portability and usefulness.
Other patents which may be relevant to the invention are:
U.S. Pat. No. 3,727,069 April 1973 Crittenden, Jr. et al. PA1 U.S. Pat. No. 3,814,438 June 1974 Baron et al. PA1 U.S. Pat. No. 4,770,527 September 1988 Park PA1 U.S. Pat. No. 4,949,972 August 1990 Goodwin et al. PA1 U.S. Pat. No. 4,972,171 November 1990 Johnson et al.